It's not a BAD thing to go through the vacuum system and replace the rubber connectors, 3-way and 4-way's. But you can also gain a lot by being more methodical and testing the various systems. Check out this door lock diagnosis guide I wrote. It was done on an earlier W123, a 1979, but the concepts are very similar for your door lock system and for other vacuum systems on your car.
https://www.ifixit.com/Guide/Mercedes+W123+Vacuum+Lock+System+Diagnosis+Technique/20201
Someone else would need to chime in on the SLS. Best of luck and congrats on the new car!